7132 ‎(2)‎

• UCREFRP Catalog Number: 7132
• Author: Jensen, B. L.
• Title: Culture Techniques for Selected Colorado River Imperiled Fishes.
• USFW Year: 1983.
• USFW - Doc Type: December 6-8, 1983.
• Copyright Material: YES

from the fished zone, the fish frequently
failed to enter the zone of action of the field
at all, but moved at a distance of 3-5 m
from the anterior edge of the electrodes or
sometimes disappeared from the trawl.
Probably in these cases a conditioned reflex
had developed in the fish.
In mackerels, which were also frequently
found in trawl catches, the manifestation of
defensive behavioral reactions during the
action of the current was similar in general
lines to that of round scad lecapterus
pgnctatus and Sardinella. Their distinguish-
ing features were: greater speed of depart-
ure from the zone of excitation, more pro-
nounced urge to leave the trawl through the
mouth, and also less resistance to the ac-
tion of the electric current. For instance,
when the current was switched on individual
fish rushed forward and after several sec-
onds disappeared from'the field of vision.
In view of the larger size of the mackerel
(up to 30 cm) the zone of electro-narcosis
was larger for them than for other fish,
and the time of travel in the space between
the electrodes was reduced.
Features of defensive behavior and reac-
tions of fish in the "horizontal electric
field". A diagram of the movement of fish
with the switching on of the current with
parameters f = 20-25 Hz; Ja = 4-6 kA,
T = 1.32 cosec is given on Fig. 2. The
main feature of the manifestation of defen-
sive reactions during the action of the cur-
rent is the urge of fish to leave the exciting
and "dangerous" zone of the space between
the electrodes and to accumulate in the
"shadow zones". In zone A when the cur-
rent was switched on, the fish performed a
rapid, shallow turn forward and downward
and moved 1.5-2 in forward where a dense
school had remained throughout the time
of the action of the current. In the space
between the electrodes in zone B, the fish
also completed a turn forward and down-
ward, and left the zone of action of the
electric field through the central portion of
the anterior electrode, increasing the
numbers in the group of fish which had left
zone A.
As our observations show, with the use
of ring electrodes defensive "escape" reac-
tions and the "'optomotor reaction", which
helped the fish to leave the space between
the electrodes, were also manifested. In
this case, the anode electrotaxis reaction
imposed a somewhat different stamp on the
manner of departure and the pattern of be-
havior of fish generally in this trawl elec-
trification system. The fish completed a
shallow turn forward and downward, attempt-
ing to move into the central portion of the
ring electrodes, where the tension of the
electric field was lower. The fish which had
approached to within 20-30 cm of the pos-
terior electrode (anode) exited through it
out of the trawl, returning immediately into
the trawl. Some fish actually came into
contact with the electrode with subsequent
instantaneous electro-narcosis (shock).
Visually the anode can always be distinguished
from the cathode by the narcotized fish en-
meshed and hanging from the webbing of the
trawl.
It is interesting to note that with the entry
into the space between the electrodes of fish
of different sizes, for instance sardinels
16-18 and 7-8 cm long, the young of these
fish received only a weak stimulus when the
current was switched on, approximately at
the level of the minimum reaction. They.
moved in the field for 20-30 seconds, after
which they began to leave the trawl in the
main through the mesh of the webbing, sink-
ing down to the bottom where they grouped
in dense schools which followed the trawl for
some time, gradually tiring and drifting
backwards out of the field of vision. At that
moment the adult fish either departed for-
ward through the center of the electrode or
were carried under the narcotic influence of
the current backward in the direction of the
codend. These observations show that the
influence of the pulsed current on the fish is
of a selective nature.
When the current was kept on, the fish
moving behind zone C gradually entered the
central portion of the positive ring electrode.
The stimulation of the fish in the electric
field was clearly noticeable from the charac-
teristic luminescence of the sides of the body.
With the decrease in the area fished by the
electric field, f, e. , with the transfer of the
electrodes to the part in front of the codend
(as a result of which the strength of the elec-
tric field increased in the space between
the electrodes) or with the increase in the
voltage fed to the electrodes of the trawl,
the fish in the space between the electrodes
were rapidly narcotized and drifted passively
into the codend of the trawl.
Discussion
With the action of an electric current with
parameters f = 20-25 Hz; Ja = 4-6 kA; T =
= 1.3-1.6 cosec, the pattern of the manifes-
tation of defensive behavioral reactions is
more varied and more clearly expressed by
comparison with the defensive reactions of
310
fish in the zone fished by the customary
non-electrified trawl. On entering the ordi-
nary trawl, the fish reorientate themselves
and move in it at a trawling speed of up to
4.5 knots for a long time (around 1 hour)
without visible signs of exhaustion and exci-
tation (Korotkov and Kuz'mina, 1972). They
only begin to sense danger in the narrowed
part, I. e. , in front of the codend of the
trawl where their defensive reactions origi-
nate (escape, departure through the mesh,
etc. ). The action of the electric current
of the parameters mentioned provokes the
manifestation of defensive reactions in
almost the whole of the space between the
electrodes.
The behavioral reactions of the fish ex-
amined can be explained from the point of
view of natural responses to dangers en-
countered in nature. For instance, the
"escape reaction" described by us, by
which pelagic fish respond to sudden excita-
tion by the current, has its natural ecologi-
cal analog. It is known that under natural
conditions many pelagic fish attempt to go
into the depths when frightened. By so
doing, they acquire the possibility of free-
dom of movement in space, which ensures
the manifestation of their defensive role to
the greatest extent (Radakov, 1961, 1970).
On the other hand, the crowding together
of fish during their departure from the zone
of excitation of the electric field under
natural conditions increases the disorienta-
tion of predators whose main sense organ
is the visual one, giving them no possibility
of concentrating on individual fish (Radakov,
1970; Hobson, 1968). It is necessary to
allow for the circumstance that the action
of the fishing gear itself as a complex
stimulus conditions the pattern of behavior
of fish in the trawl and raises the threshold
of reaction and resistance to the effect of
the pulsed current. Thus for instance, it
was established by our laboratory experi-
ments that the "immobilization" of fish by
optomotor reaction in the aquarium requires
such a high voltage in the electric field as
to provoke an anode electrotaxis reaction in
fish (Danyulite and Maksimov, 1974).
The purpose of the creation of an electric
field in the trawl is to neutralize the mani-
festation of the defensive reactions mentioned,
to accelerate the process of formation of the
catch in the codend of the trawl and to pre-
vent the fish from leaving at the time of
hauling in the trawl. Moreover, the creation
as far as possible of a narrow zone of exci-
tation around the electrodes which would
result in the rapid filling of the space be-
tween the electrodes with new batches of fish
is a necessary condition. Our recent re-
search in this area have made it possible to
increase the volume of water in the trawl
in which rapid disorientation of the fish
occurs and to decrease the manifestation of
defensive reactions by the choice of electri-
fication system and parameters of pulsed
electrical current.
Submitted July 7, 1975
LITERATURE CITED
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